1. Field of the Invention
The present invention generally relates to detection of changes in a property of a liquid that is mixed with one or more reagents. This invention is particularly concerned with detecting changes in viscosity of human blood that is mixed with blood viscosity changing reagents such as heparin and protamine.
2. Statement of Problem
The ability to detect changes in a property of a liquid that has been placed under the influence of a reagent that is capable of changing that property has great practical value. Changes in viscosity, translucence, color, electrical conductivity, optical density, chemical component concentration, and many other properties have been used in a wide variety of tests. For example, detection of changes in the viscosity of liquids such as blood, food products, and various other liquid compositions (e.g., industrial fluids, oil well injection fluids, etc.) form the basis of many very practical tests.
Indeed, the ability to detect changes in the viscosity of human blood can even have life and death consequences. This follows from the fact that a proper balance between normal hemostasis and coagulation or anticoagulation is absolutely essential in maintaining the integrity of the human circulatory systemxe2x80x94and in stopping both external and internal bleeding. It is, however, sometimes necessary to modify the natural coagulation system, either by increasing or decreasing the rate of blood coagulation. During open heart surgery for example, a patient is usually supported by a heart/lung bypass machine that provides extracorporeal blood circulation while the heart is stopped. To prevent blood from clotting upon exposure to the bypass system, the patient is treated with high doses of heparin, a naturally occurring substance that significantly prolongs the clotting time of blood. When the time comes to remove the patient from the heart/lung bypass machine, however, it is desirable for the patient""s blood to regain its normal coagulation characteristics so that it will again be able to clot and assist in healing incisions and stopping internal or external bleeding. This reversal of the effects of heparin is achieved by treating the patient""s blood with an anticoagulant-reversing substance (e.g., protamine) capable of neutralizing heparin or other anticoagulating substances.
To successfully maintain anticoagulation during a surgical procedure, and neutralize the heparin at the conclusion of surgery, it is highly desirable to be able to quickly and accurately determine the concentration of heparin in the patient""s blood. Unfortunately, since the activity of heparin varies significantly from batch to batch, and from patient to patient, these determinations cannot be made simply on the basis of the amount of heparin administered. Protamine also varies in potency from batch to batch and from patient to patient. Furthermore, protamine itself can act as an anticoagulant. Thus, for optimal reversal of a given heparin action, it is essential to use only that amount of protamine that will directly neutralize the amount of active heparin in a particular patient""s blood.
Such reversals of a heparin action are detected by dose-response tests which measure changes in blood clotting time in response to differing doses of anticoagulant in order to determine the correct dose of anticoagulant for a particular patient. Clotting time or activated clotting time tests are used to determine whether a patient""s blood has achieved the desired level of anticoagulation. Heparin/protamine (anticoagulant/neutralizer) titration tests have been developed to provide accurate determinations of heparin (anticoagulant) levels. Such tests are based on measuring the time necessary for the blood to coagulate. Consequently, these titration tests measure coagulation time as an empirical measure of blood viscosity. These titration tests are accurate; but they have three major drawbacks. They require relatively long times to conduct, they require relatively large blood samples and they are subject to variable results and inaccuracies due to operator related variances. Consequently, various alternative methods and apparatus have been proposed to address these drawbacks.
By way of example only, U.S. Pat. No. 5,629,209 (xe2x80x9cthe ""209 patentxe2x80x9d) discloses apparatus and methods for detecting changes in human blood viscosity through use of cartridges that, in conjunction with a test apparatus, are used to detect changes in blood viscosity. Heparinized blood is introduced into the cartridge through an injection port and fills the blood receiving/dispensing reservoir. The blood then moves from the reservoir through at least one conduit into at least one blood-receiving chamber where it is subjected to a viscosity test. In this test, a freely movable ferromagnetic object is placed within the blood-receiving chamber. The ferromagnetic object is moved up and down by an electromagnet in the test apparatus. Changes in the viscosity of the blood through which the ferromagnetic object falls are detected by determining the position of the ferromagnetic object in the blood-receiving chamber over a given time period or a given number of rises and falls of the ferromagnetic object. The incoming blood sample can be mixed with a blood viscosity altering agent (e.g., protamine) as it passes through the conduit to the blood-receiving chamber. Any air in the fluid communication system in front of the incoming blood sample is vented through an air vent/fluid plug device.
Applicants are co-inventors in the ""209 patent and regard it as the closest prior art to the present invention. Therefore, its teachings are hereby fully incorporated into the present patent disclosure. The apparatus and methods described in the ""209 patent are concerned with the same general issues e.g., test accuracy, test speed and operator safety that are further addressed in the present patent disclosure. Applicants"" continued concern for these issues follows from the fact that the apparatus and methods of the ""209 patent proved to have various drawbacks. These drawbacks have been eliminated or greatly diminished by the present invention. Many of these drawbacks were ultimately traced to the fact that a blood sample and the reagents (e.g., protamine) mixed into that blood sample by the apparatus and methods of the ""209 patent were not uniformly mixed. This lack of uniformity of mixture resulted in test readings that sometimes proved to be unreliable. It would therefore be desirable to continue to employ, and enhance, the advantages originally brought about by the apparatus and methods taught in the ""209 patent, while improving upon the reliability of the tests in which they are used. It also would be desirable to use these improvements in conducting other tests (e.g., those based upon changes in translucence, color, electrical conductivity, optical density, component concentration, electromotive response, etc.) on liquids other than human blood.
As was the case with the apparatus and methods of the ""209 patent, the present invention is carried out through use of a disposable cartridge containing one or more simple testing chambers. This use of multiple chambers allows several tests to be performed simultaneously using uniform samples in a single cartridge. Thus, a second, third, etc. test carried out in that single cartridge can be a duplication of another test (to ensure greater reliability), or two or more entirely different tests can be conducted simultaneously. Here again, the amount of fluid contained within each test chamber is automatically determined. Hence, it will not vary from chamber to chamber or from test to test. The disposable cartridges of the present invention also are relatively small in size (thereby reducing the amount of storage space needed) and, likewise, relatively easy and inexpensive to manufacture.
The apparatus and methods of the present patent disclosure can be used in virtually any test where a reagent is mixed with a liquid sample and then tested for some change in a property of the resulting liquid/reagent mixture. The present apparatus and methods are particularly well suited for clotting time tests, dose-response tests, and especially titration tests on human blood taken from patients undergoing anticoagulation therapy during heart/lung bypass surgery. The apparatus and methods of the present invention are, however, much better able to detect changes in a property of a liquid relative to the results obtained with the apparatus and methods taught by the ""209 patent. This improved accuracy also serves to expand the possible uses of the cartridges of the present invention to test where blood is not the liquid being tested. The basis for these improved test results will be discussed hereinafter in far greater detail.
A test procedure of the present patent disclosure commences when a liquid sample to be tested is introduced, under pressure, into a cartridge made according to the teachings of this patent disclosure. The cartridge can be loaded with a liquid sample when the cartridge is outside of the test machine or after the cartridge is inserted in said machine. It is generally preferred to load the cartridge after it is placed in the test machine. The fluid injection can be done manually or automatically through an injection port in said cartridge. Loading the cartridge by means of a syringe is a preferred method of introducing a liquid such as a blood sample into the cartridge.
In any case, the pressured liquid to be tested by the present apparatus first flows into a fluid receiving/dispensing reservoir contained within the body of the present cartridge. From the fluid receiving/dispensing reservoir the pressured fluid moves through a conduit leading to a fluid-receiving chamber. The cartridge can have as few as one fluid-receiving chamber. It is preferred, however, that the fluid receiving/dispensing reservoir is provided with one or more (preferably from two to twelve and most preferably from four to six) separate conduits that each lead to a respective fluid-receiving chamber. Such a reservoir/conduit/fluid-receiving chamber fluid communication system enables all the chambers to be filled more or less simultaneously. In some of the more preferred embodiments of this invention, the fluid communication between the fluid receiving/dispensing reservoir and the fluid-receiving chamber(s) is via a conduit having a constricted passage. As was the case in the cartridges of the ""209 patent, each fluid-receiving chamber is further provided with an air vent/fluid plug device that is in fluid communication with a given fluid-receiving chamber. Thus, any air contained within the reservoir, conduit, and fluid-receiving chamber is driven before the incoming liquid and vented through one or more of these air vent/fluid plug device(s) as fluid enters and passes through the system. Again the air vent/fluid plug device, although porous to air, is non-porous to a liquid; thus, when the liquid sample reaches a given air vent/fluid plug device, it establishes a liquid lock and thereby prevents further movement of the liquid i.e., out of the cartridge via a given vent/fluid plug.
The fluid (air plus liquid) flow paths from the receiving/dispensing reservoir, through a given conduit and into a given fluid receiving chamber in the cartridge of the present invention do however differ from the analogous path(s) described in the ""209 patent. At first glance, these differences may not appear to be radical or extensive. Nonetheless, applicants have found that their use has a very significant effect on the reliability of test results produced by use of the cartridges of this patent disclosure vis-à-vis the results produced by the cartridges described in the ""209 patent.
There are at least three physical differences between the cartridges taught in the ""209 patent and the cartridges of the present invention. Applicants have found that each of these three differences serves, in its own right, to improve upon the test results produced by the cartridges taught in the ""209 patent. The combined use of 2 or 3 of these differences produces incrementally better and better results with each added feature. The first physical difference between the ""209 cartridges and the cartridges of the present patent disclosure is the fact that the conduits located between the fluid receiving/dispensing chamber and a given fluid-receiving chamber in the present invention are provided with a constricted passage section. This constricted passage section is located between a given fluid-receiving chamber and the remainder of the conduit that feeds into the given fluid-receiving chamber from the fluid receiving/dispensing chamber. In the more preferred embodiments of this invention, the constricted passage will have a cross sectional area that is from about 20 to about 80 percent of the cross sectional area of the conduit that feeds fluid into that constricted passage. Preferably the conduits of the present cartridges will have cross sectional areas of from about one square millimeter (1 mil2) to about three square millimeters (3 mil2). Constricted passages having cross sectional areas of from about 20 to about 50 percent of that of its feed conduit are even more preferred. Such a constricted passage (owing to principles associated with Bernoulli""s law) serves to increase the velocity of fluid flow through said constricted passage. Applicants have found that this increase in fluid velocity serves to significantly increase the degree of mixing between a liquid and any reagent mixed into that liquid.
The reagent can be mixed with the liquid before said liquid enters the cartridge, or the reagent be positioned in the conduit such that it comes into contact with the incoming liquid before the resulting liquid/reagent mixture enters the constricted passage. In some of the more preferred embodiments of this invention, however, the reagent is placed in the constricted passage itself. Under any of these liquid/reagent mixing circumstances, the increase in liquid velocity in the restricted passage serves to mix the reagent with the liquid much more thoroughly than the system taught in the ""209 patent wherein the conduit between the fluid receiving/dispensing reservoir and the fluid-receiving chamber has no such constricted passage.
The second physical difference between the cartridges taught in the ""209 patent and those employed in the present invention is the fact that the fluids introduced into the fluid-receiving chamber(s) of the present invention are introduced into said chamber(s) in a substantially tangential flow pattern. That is to say that the incoming fluid flow is not directed at the center of a fluid-receiving chamber, as it is under the teachings of the ""209 patent (see for example FIG. 9 of said ""209 patent), but rather is directed more toward the periphery of said fluid-receiving chamber. For the purposes of this patent disclosure, the expression xe2x80x9csubstantially tangential flow patternxe2x80x9d can be taken to mean that the incoming flow is aimed at a point in the fluid-receiving chamber that is more than about half way beyond the center of the fluid-receiving chamber in a direction toward an outer wall of said fluid-receiving chamber. In some more preferred embodiments of this invention, the incoming fluid flow will be directed in a path that is substantially tangent to a fluid-receiving chamber wall that is round in configuration. In other preferred embodiments of this invention, this tangential flow also will be directed into an upper portion of the fluid-receiving chamber e.g., near its roof region as opposed to its base region (see for example, FIG. 14). In yet another preferred embodiment of this invention, the incoming fluid flow will enter a given fluid-receiving chamber by an entry port that is elliptical in shape (as opposed to the round entry ports implicit in the ""209 patent).
The third physical difference between the cartridges of this patent disclosure and those taught in the ""209 patent is that the air vent/fluid plug device of the present invention is placed in fluid communication with the fluid-receiving chamber by means of a fluid exit conduit that is mounted in a substantially tangent manner with respect to a wall of said fluid-receiving chamber. That is to say that fluid flow out of the fluid-receiving chamber via the fluid exit conduit takes place at an angle that is substantially tangent to an external wall of the fluid-receiving chamber rather than substantially perpendicular to that external wall. Applicants have found that this fluid exit arrangement better serves to purge air from the fluid-receiving chamber as incoming liquid fills said fluid-receiving chamber. In other preferred embodiments of this invention, this exiting tangential flow also will be directed out of an upper portion of the fluid-receiving chamber (near its roof region, as opposed to its base region) and into an upper region of a vent/fluid plug device (near its roof region) as opposed to a base region of said vent/fluid plug device (see generally FIG. 14). In yet another preferred embodiment of this invention, the exiting fluid flow will leave a fluid-receiving chamber by an exit port that also is elliptical in shape (again, as opposed to the round shapes implicit for these comparable chamber exit ports in the ""209 patent). In still other preferred embodiments of this invention, the fluid exit port leading from a fluid-receiving chamber to a vent/fluid plug device will be substantially opposite to the position of the fluid entry port leading into said fluid-receiving chamber.
Again, applicants have found that each of the above noted fluid flow features, in its own right, will help a given test apparatus produce more accurate test results. Of these three differences between the cartridges of the present invention and those of the ""209 patent, use of a constricted passage is the somewhat more influential. In any case, use of two of these fluid flow related features (e.g., (1) constricted passage plus tangential flow into chamber, (2) constricted passage plus tangential flow out of chamber, (3) tangential flow into and out of chamber, etc.) will produce better results than use of just one of them. In the same vein, use of all three of these fluid flow features will produce still better test results.
Moreover, these cumulative improvements appear to be the case, regardless of the nature of the liquid being tested, regardless of the nature of the reagent mixed with the liquid in the test cartridges of this patent disclosure and regardless of the type test performed on a liquid/reagent mixture in the fluid-receiving chamber. Thus, the cartridges of this patent disclosure can be used in virtually any test wherein changes in a property of a liquid/reagent mixture is to be measured e.g., changes in viscosity, translucence, color, electrical conductivity, optical density, fluid component concentration, electromagnetic response and so on. Thus, even though a biological fluid (i.e., blood) is used as the primary example in this patent disclosure, other fluids that must be mixed with a reagent in order to perform a test (e.g., other xe2x80x9cbiologicalxe2x80x9d fluids such as urine, DNA suspensions, as well as xe2x80x9cnon-biologicalxe2x80x9d fluids, e.g., industrial chemical compositions, laboratory chemical compositions) can be tested using the hereindescribed cartridge features, geometries and test procedures.
Another physical difference between the cartridge devices taught by the ""209 patent and those of the present patent disclosure is primarily concerned with better (e.g., safer, simpler, etc.) handling procedures (as opposed to better sample mixing procedures) for the cartridge, especially when it is inserted into, and removed from, the machine in which a test is performed. In the case of the present invention, a syringe used to inject a fluid sample into a cartridge can also serve as a xe2x80x9chandlexe2x80x9d for the cartridge, thereby eliminating the need for the operator to touch the cartridge with his (her) hands. This less than desirable circumstance was implicit in the use of the cartridges taught in the ""209 patent. Under the teachings and methods of the present patent disclosure, the syringe handle and cartridge are preferably inserted into the test machine and thereafter disposed of as a single unit. Thus, this difference (the use of a syringe as a xe2x80x9chandlexe2x80x9d for the cartridge) does not effect test results, but rather improves upon the ease and safety associated with loading and unloading the present cartridges into and out of a given test machine. To this end, the fluid receiving/dispensing reservoir of the cartridge receives the subject fluid through an injection port/syringe connector that leads from the top side of the cartridge near its rear end. Preferably an injection port/syringe connector is attached to the cartridge at an upwardly directed angle. Thus, when a syringe is connected to the injection port/syringe connector, the syringe serves as a handle for inserting the attached cartridge into the test machine and, upon completion of the test, taking said cartridge back out the machine. Again, the syringe/handle and the cartridge are most preferably disposed of in this assembled or unified state. Thus, the test machine operator is better protected from contact with the fluid being tested relative to the human finger operated insertion method suggested in the ""209 patent.
To these ends, the nose of a syringe can be designed to be tightly compression fitted into the cartridge""s injection port in order to maintain this assembled state. In yet another preferred embodiment of this invention, the injection port and the nose of the syringe will be provided with an interlocking device such as a threading systems or so-called xe2x80x9cbayonetxe2x80x9d locking device whose operation involves inserting a nub or other projection on one element (e.g., the nose of the syringe) into a keyway having a laterally positioned projection receiver. Thus, the nub (or other projection) is forced into the projection receiver by rotating the fully inserted syringe about 90xc2x0 in the cartridge injection port. These and other advantages, features, and objects of the present invention will be more readily understood in view of the following more detailed descriptions and the drawings.